777 ground spoiler deployment
 

Question for the smart 777 folks.

I’ve noticed that on landing, the 777 nose isn’t overly eager to come down. I’ve seen from a few videos that on touchdown, the spoilers only partially deflect, then fully deflect after a short delay (see attached video at 10:25).


I can’t find anything in my company’s manuals. Can someone provide some information (preferably with a reference) as to what triggers full extension please?

Thanks in advance.

Lots of discussion in an airliners dot net thread but for some reason I can't paste the URL here.

airliners dot net slash forum slash viewtopic dot php ?t=775571

A long time ago I did some work on 777-300 displays and remember there was was logic based on bogie/truck tilt. Too long ago to remember the details.

Thanks for that. Interesting response in post #7. That could well be it. Would love to see a reference for it if anyone has one.



(Also, thanks for the link. For some reason, it doesn't allow me to post it either)

Yes, as described in that post, ground spoiler deployment is affected by the PFC speedbrake inhibit function. The inhibit function operates when the pitch attitude is more than 2° with the aircraft on the ground, or during the first 1.25 seconds after main landing gear air-to-ground transition. On touchdown, the auto speedbrake control commands the speedbrake lever to move rearwards to deploy the spoilers. With the inhibit function active, outboard spoilers 2, 5, 10 and 13 do not deploy, and the inboard spoilers (6, 7, 8 and 9) are limited to 20°. The mechanically controlled spoilers (4 and 11) are not affected by the inhibit function - they only deploy when the speedbrake lever moves past 54°.

Of course none of this is described in the pilot manuals. It's covered in the B777 Aircraft Maintenance Manual, 27-61-00, under "Spoiler and Speedbrake Control - Functional Description", and in the maintenance training manuals based on that document. Check with your airline.

Other aircraft have delayed ground spoiler deflection. The A330/340 limits spoiler deflection to ensure a controlled touchdown of the MLG front wheels of the very tilted bogie to avoid a big thump. At MLG front wheel touchdown the spoilers fully deploy. If I remember correctly the DC10 ground spoilers initially deployed at a slower rate then more rapidly after they reached a certain point.

Thanks for the information gents. Will look up the AMM reference.

MD-11 spoilers, if armed, extend to 30 deg limit on wheel spin and go to 60 deg limit when the NLG indicates on-ground. I see no indication of a rate change in 27-63 schematics. I would expect DC-10 to be similar but I have no data.

Speedbrake Inhibit Function
The speedbrake inhibit function has an effect on the ground spoiler speedbrake commands.
The function receives main landing gear on the ground signal from the PSEU and the pitch attitude from the ADIRU.
The function also monitors the position of the speedbrake lever.

The speedbrake inhibit function operates when the pitch attitude is more than 2 degrees with the airplane on the ground or during the first 1.25 seconds after a main landing gear air to ground transition.
When there is a speedbrake lever command, the outboard spoilers 2, 5, 10 and 13 do not deploy.
The PFCs limit the inboard spoilers 6, 7, 8, and 9 to 20 degrees until the speedbrake inhibit function is no longer active.